This invention pertains generally to a composition of matter suitable for removing hydrogen from gaseous mixtures including hydrogen and oxygen and particularly to a composition suitable for removing hydrogen from gaseous mixtures containing hydrogen and oxygen, wherein the concentration of hydrogen is within the explosive range.
Hydrogen can be produced from corrosion of metals by atmospheric gases or stray electric currents; from batteries, operating in normal or abnormal condition; and from leaky hydrogen piping. The accumulation of hydrogen can present a significant fire hazard and in the presence of oxygen can represent a potential explosion hazard particularly in sealed components.
It has long been known that hydrogen absorbing materials, known as getters, can be used to counteract hydrogen accumulation. Ayers et al. discuss the use of active metals such as zirconium or titanium, and alloys thereof in U.S. Pat. No. 4,512,721. These metals are capable of maintaining low hydrogen partial pressures but have the disadvantage of requiring high temperatures for initial activation and/or ongoing operation because of the necessity to diffuse surface contaminants into the bulk metal thereby providing a fresh surface for continued hydrogen absorption. Furthermore, in the presence of oxygen the hydrogen/oxygen mixture can react explosively on contact with these getter materials.
Labaton, in U.S. Pat. No. 4,886,048, describes another means for removing hydrogen by reacting the hydrogen with oxygen to form water, in the presence of a noble metal catalyst such as palladium, and trapping the water on a water absorbing material such as a molecular sieve. However, hydrogen getters of this type are expensive, bulky, and capable of causing a detonation if the concentrations of hydrogen and oxygen are within the explosive range, generally defined as mixtures of hydrogen and oxygen, wherein the hydrogen concentration is greater than about 6 vol % and less than about 67 vol %.
Conventional hydrogen getters, such as those described in the above-referenced patents are expensive, can require special operating conditions such as high temperature regimes or ancillary reactants in order to maintain low hydrogen partial pressures, generally will not work well or at all in the presence of water, may require the presence of oxygen, be poisoned by oxygen, and may pose significant safety hazards, including fire and explosion if handled improperly, for example by exposure to air.
It is well known in the art that unsaturated carbon-carbon bonds (i.e., double or triple bonds between carbon atoms) can be reduced by hydrogen and its isotopes in the presence of an appropriate catalyst to form an alkane. Anderson et al. in U.S. Pat. Nos. 3,896,042 and 3,963,826 and Harrah et al. in U.S. Pat. No. 4,405,487 disclose the use of solid acetylenic compounds (i.e., organic compounds having carbon-carbon triple bonds) combined with various Group VIII metal catalysts to irreversibly remove hydrogen over the temperature range -50.degree. C. to 110.degree. C. Shepodd et al. in co-pending application Ser. Nos. 08/424,775, 08/647,093, and 08/716,752 disclose other compositions of unsaturated organic compounds and noble metal catalysts, preferably Pd, suitable for gettering hydrogen under a variety of conditions. However, the aforementioned hydrogen getter compositions suffer from the drawback that the addition of hydrogen to unsaturated bonds can cause significant changes in physical properties of the organic compound, such as melting point, which may be undesirable
The generation and accumulation of hydrogen is a concern in sealed electronic devices where hydrogen accumulation could become a safety hazard. One particular concern is found in portable lighting devices such as lanterns and flashlights which employ batteries having aqueous electrolytes and which must provide means for safely eliminating hydrogen evolved as the result of corrosion reactions, charging, inadvertent battery reversal, etc. As taught in U.S. Pat. Nos. 5,349,507, and 5,535,107 various solutions comprising the use of venting means which may or may not be coupled with a catalyst pellet to effect catalytic recombination of hydrogen and oxygen to form water have been proposed to remove hydrogen overpressure from these systems.
Of particular concern, however, is the presence of both hydrogen and oxygen because of the potential for an explosion in the case of a static electric discharge or a spark as well as in the presence of a noble metal hydrogenation catalyst. It will be appreciated by those skilled in the art, that the reaction between hydrogen and oxygen in the presence of a hydrogenation catalyst is rapid and exothermic and over a wide range of concentrations can be explosive because the catalyst temperature can rise from the heat of reaction above the ignition temperature of the mixture of hydrogen and oxygen gases. What is desired is a means for safely removing hydrogen from an atmosphere which contains oxygen without the danger of explosion. The present invention, by mediating the reaction between hydrogen and oxygen, in the presence of a hydrogenation catalyst, to form water, provides a means for removing hydrogen from atmospheres including a mixture of hydrogen and oxygen particularly at concentrations of hydrogen within the explosive range.